This invention relates to an improved method of controlling the temperature of a substrate clamped to a substrate support in a deposition chamber.
As semiconductor substrates become larger, and devices formed therein become smaller, new materials and processes must be developed for making these devices. For example, the use of aluminum, which has long been used to make conductive paths and contacts, is being supplanted by copper, which is more conductive and thus has a lower resistivity. Further, copper has superior electromigration properties than does aluminum, even, for example, aluminum doped with silicon. Thus copper has some superior properties for integrated circuits.
A problem with using larger substrates, e.g., silicon wafers, is that processing uniformities are more difficult to maintain across the larger wafer; processing must be uniform across the diameter of the wafer in order to produce devices that are the same across the wafer, irrespective of their position on the wafer. As 8 inch diameter wafers are replaced with wafers of approximately 12 inches in diameter (200 mm diameter), this is not a trivial task.
In preparation for the deposition of copper onto a previously deposited and etched dielectric insulative or other layer, conventionally a barrier layer is deposited between the previously deposited film and the copper layer. The barrier layer can be made of Ta, TaN, W, WNx and the like. A seed layer of copper is then deposited onto the barrier layer by sputter deposition, which is followed by electroplating of copper onto the substrate to a finished thickness.
The morphology of the copper seed layer is very important; if the seed layer is rough or bumpy or non-uniform in thickness across the layer, the overlying electroplated copper layer will also be non-uniform, particularly since the copper layers deposited inside the vias and contact openings may be very thin.
A seed layer of copper can be deposited in a sputter deposition reactor. A suitable sputter deposition reactor has a biasable substrate support electrode that can be cooled or heated with a flow of chilled or heated fluid therethrough. The wafer temperature can be maintained close to that of the support electrode by a flow of backside gas, such as about 15 sccm of argon or other inert gas which is passed between the wafer support and the wafer.
A suitable chamber for depositing a copper seed layer is shown in FIG. 1 in a schematic cross sectional view. This chamber is known as an ionized metal plasma (IMP(trademark)) a trademark of Applied Materials, Inc. chamber
The IMP(trademark) chamber 100 as shown in FIG. 1 comprises a target 104 comprising the material to be sputtered, i.e., copper or other metal, which is mounted on the lid 102 of the chamber. Magnets 106 are mounted on the lid 102 behind the target 104. A substrate support 112 is movable vertically within the chamber and includes an upper support surface 105 for supporting a substrate 110. The support member 112 is mounted on an elevator 113 connected to a motor 114 that raises and lowers the support 112 between a lowered loading/unloading position and a raised, processing position. An opening 108 in the chamber wall permits entry and egress of the substrate prior to and after processing. A lift motor 118 raises and lowers pins 120 mounted in the substrate support 112, which in turn raise and lower the substrate 110 to and from the upper support surface 105 of the substrate support 112.
A coil 122 provides inductive magnetic fields in the chamber to generate and maintain a higher density plasma between the target 104 and the substrate 110 than would be possible with standard magnetron sputtering of the target 104. The coil 122 is preferably a flat surface facing inward to the chamber and composed of the same material as the target, as it too will be sputtered to provide deposition material to the substrate. A clamp ring 128 is mounted between the coil 122 and the substrate support 112 which shields an outer edge and the backside of the substrate 110 from sputtered material in the chamber when the substrate 110 is raised into a processing position. In the processing position, the substrate support 112 is raised upwardly into the clamp ring 128.
Three power sources are used in the chamber 100. A first power source 130 delivers power to the target 104 to cause the formation of a plasma from a processing gas through gas inlet 136. A second power source 132, preferably an RF power source, supplies power to the coil 122 to increase the density of the plasma. A third power source 134 biases the substrate support 112 and thereby provides directional attraction of the ionized sputtered target material toward the substrate 110. A vacuum pump 146 coupled to an exhaust pipe 148, in combination with an argon supply (including argon passing under the substrate to and into the chamber) maintain the desired pressure in the chamber.
A controller 149 controls the functions of the power supplies, lift motors, vacuum pump and other chamber components and functions.
In operation, a robot delivers a substrate 110 to the chamber 100 through the opening 108. The pins 120 are extended upwardly to lift the substrate 110 from the robot, which is then retracted from the chamber 100. The opening 108 is then sealed. The pins 120 lower the substrate 110 to the upper surface 105 of the substrate support 112. The substrate support 112 is then raised so that the substrate 110 engages the clamp ring 128. One or more plasma gases are introduced into the chamber 100 through gas inlet 136 and a plasma is generated between the target 104 and the substrate support 112 with power from the first power source 130.
The second power source 132 delivers power to the coil 122 to densify the plasma and ionize at least an additional portion of the sputtered target material from the target 104. The substrate support 112 is then biased by the third power source 134, so that the sputtered ionized particles are accelerated towards the substrate 110. A flow of gas is initiated in the substrate support to heat or cool the substrate 110 during deposition. After deposition is complete, the substrate support is lowered to permit retrieval of the processed substrate and to deliver another substrate for processing.
The substrate support 112 also includes a passage for the flow of an inert gas to the surface 105 of the support 112. The gas can be supplied from a single opening in the support 112, or the gas can be led through channels in the support surface 105 (not shown) to permit more uniform heating or cooling of the substrate 110.
However, the chamber 100 produces a non-uniform deposit of a seed layer of copper onto the substrate. The deposited copper seed layer is essentially smooth at the center of the substrate, but is very rough nearer the edges of the substrate. It was believed that this non-uniformity was caused by heating of the clamp ring 128 over time (to 300-400xc2x0 C.). However, the rough deposits extend up to 2.5 inches from the edge of the substrate, far more than the width that the clamp ring rests on the substrate. Thus the temperature of the clamp ring does not explain the problem or suggest a solution.
A method for improving the uniformity of a deposited copper seed layer across a substrate would be highly desirable.
We have found that by maintaining a minimum pressure of the temperature control gas between the substrate support and the substrate of at least 15 torr, improved uniformity of the thickness and morphology of a sputter deposited layer metal seed can be achieved.